Method of making composite thermionically emissive cathode material



June 21. 1955 A. H. cHlLnERs l-:rAL METHOD OF' MAKING COMPOSITETHERMIONICALLY EMIssIvE cATHoDE MATERIAL Filed Nov. 1s, 1952 .W Y' "a,

jV l'r Pateteddune 271'.;

' The heaterfof this inventi'onis in many respects. simi'- 2,711,s90-METHOD F COMPOSITETHERMIONI- CALLY Alida H. Cliild'ers,'New York, andDaniel Gold, Brooklyn, N. Y., assignors to Sylvania Electric' Products,luci, a corporation. of Massachusetts components i the most importantdistinctionr being 5 in sulating coating of Alundum 12u which is. inturni-directsrciaims. (ci. .204--1815 1y Coated with a nickei s111114.`This. spin tumcoated with a normalroxide lcoating'usuallyfusedforicathodesrf n which is vshown in the drawings .at 16". lrrtheVer'nbodi-` This invention relatesto a quick heating cathode and 1;) mentShown hlrs 'matlerlfial its k'eplkfd` ffm a tflplleV Caftheir method ofmanufacture.k It particularly relates to bOIIae a quick heating catho-deofthe type suitable for use in electron discharge devices.` I Thecathode assemblies ofthe prior lartconsistof a cathode sleeve usuallynickel withl an insulated heater centrally located inside the sleeve.The cathode becomes effective and emits electrons` whenV the oxide Ycoated sleeve is heated toa temperature in. the neighborhood of 850 C.This Ais accomplished in the 'prior c Y n Y* l v y art cathode sleevesby passing current through the 'heatg5 @rating emPefal-ek Wlu-bsubstantlauyf IQWeF- 'Fuf' er wire and bringing it' up to a hightemperature whereupon heat waves radiate outwardly from the heatingfilament and heat up the surrounding cathode sleevef The assembly is,therefore, often called an indirectly .ffac'e whichis in contactwiththe,Alundurncoating'the t, iilamentary wire`10.v ,Itisyalso.readilyapparent .that a theindirectly heated'cathodesoftherpriorY art inasmuch that the cathode is firmly-supportedbyrthe'vinner core since it is attached directlythereto. f Thiscathodemay, ofV c,0,urse,obe produced iny many heated cathode. Althoughcathodesof this utype have 3i) WaYS-"Some Steps in' the Production '0f-V'thiscathofle Y 3; are, Vof course, the Asame as those used. innthenormal of construction ofthe prior Vart-cathode as,fforfexample`,

Y the heater wire may becoated with jthejAlundum Yelectrophoreticallyzas is- HOWbeing done in the prior'art;V

Secondly, their eiciency is not as goodv as it might be However# foncethis; has been VaCCOmPlShednt fisrfthn i i given satisfactoryservicekandare still .doing so they have obvious disadvantages in thatthey are fnot dif rectly heated and depend for their sourceof heatontheradiated heatoenergy emitted from a secondary source.

as considerable energy is lost during this transmission of heat byradiation which is one of the least eicient l heating methods. Thirdly,the construction-is not as rugged as it' might be in view of the factthat the cathn necessary to applya metaliilm'over thecoating., This 1yfrom the heating filament and fixedly from the grid 31? resulte' This'relatively. difficult in view of the fact that a' sudden i shock or jarcould disturb the; relative positions ofthe CCSSfZYKb deposited011.11116 POIQUS .Alllrldllmtogfom filament and cathode sleeve as wellas the sleeve and aODnUOUS me/tal .lmWhCh doe-Sinin Penetr the, Yporousv Alundumusing vapor deposition techniques. o One Vtechniqueofthis type is` illustratedpin Figure, 210i'V It is, therefore, anobject of this invention to prov ith-e'flrawingsfinWhichfthAlundumofefdheae 'is i 4 continuously coated with 'mckel from nickelcarbonyl .1,- The heater to be formed and'themethodV tofbeused.'y ferreddlrectly to the cathode surfacerby conduction. need notbe limited, to.they use, of* nickelkr fmmnickel y *Y carbonyl." A metal Vfilm may bemade from any metal l' Vwhichforms volatile compounds that .canberdecomposed l below the melting point ofthe heater'compone'nts or off 1. themetal,itselfygflfhedecomposition may berentirelyfn It 1s afurther object of th1s invention to `provide a 55 thesrmariorr aided. rreducing atmospheresuch *aS-i .o

hydrogen;V [Forexamplathe nietalmight befa'tantalumll metal sheathwhich'has been vapo'r'deposited, fromdanother tube elements even whenthese elements are prop'- erly mounted during the assembly period..

vide a quick heating cathode in whichthe heat is translt is a furtherobject of this invention to provide a quick heating cathode in which the-power required t0 bring the cathode up to operatingV temperature willbe substantially lower.

rugged cathode construction wherein the cathode is rmly supported by theinner heating core. Y

It is a still further object of this invention to improve "mmmipfentachlorida Y* A y or the Cathodes reliability by Controlling the'31.105' ele 60 ln accordance with the method shown inrlig'ure 2 ofments Present in the Cathode itselfthe drawings aL carrier gassuch ashelium or-nitrogen In accordance with this invention it has been foundthat these objects and other advantages incidental thereto can beobtained byv directly coatinga metal film on an insulated heater. Y Y

In the drawings which illustrate features of this Vinvention Figure l isan elevation partly in section of'a quick heating cathodeof'thisinvention. fr Figure 2 is a schematic drawing illustrating ameththis. system` is added* nickel carbonyl in gaseous `form nickelcarbonyl Aenters theV supply'1ine122wl'1erein it'is od of coating theinsulated heater wirejrwith 'a metal transported bythe carrierogas to'thecoating' area'whichV o consists .essentially of a water cooledcondenser 32. -Inlm in order to produce the quick heating cathode ofthis invention. sulated heater wirefwhiclr-is ypresent on supply spool40 lar toY an. indirectly heated type heater ofthe prior art, thatisto,` say, it .has'substantia'llyithe same number `of Y their.relative` position. ;to on'evanother theyl.

differ fonly in that Vthefnietal forming the cathode sleevefk Y itselfinsteadV of beinglf'spac'edfrom the insulatedrii'lan -mentary heater yisdirectly applied thereto.-.:-'Ifhiscan1be4` seen quitel clearly. inFigure il,ofjthe-fdrawingsw ereid/ Application Novemtier18,'19'sz,seria1 No. 321,186` 1 0 the mammary We heatefls ShOW f1-L Wth*its im' Y `VWith, aheaterr of this Atype .itoisreadily'apparentjthat v.l thecath'ode isfn'ecesrsarily quick Vheated in'view Y, of the fractthat heat. is' transferred directly l toithe cathode surf` cathode, ofthis type'will haverg'reater yetlciency than i" as the kpowerk requiredto bringdthe cathode :u'pto op-f- *i thermore, this cathode has a1ruggedizedY construction-in is more Vofa prohlemlsince the metal iilmmust'bepcon-r i ktinuous and since the jmetal must not be allowedtofpenefr f trate.' into the porous Alundum otherwisefelectricabi i odeis not firmly supported and must bespaced coaxial# 4^() 163mg?V btwilfheheater. and the cat hQde -Sul'faCQWL o ould rtaturallyleadk to theproduction' v, j

and plate if the best results are to be obtained. This is Y fof"an/aunsasftory Cathod@ In accordance VW11-5-`.

' invention itl has vbeen T 'found1that this'fmetalmay, suer,

isadmitted toV the'` system from" `tank 20, perfnr'littedto'vr 4;. ilowinto supply-line ZZ''at `a constant ytlow.V rate. VTo

which is obtained by vaporizing lthenickel carbonyl from its liquid formwhich is'keptin reservoir 3ti. This can Y be heated to ay suitableVtemperature toggivexthe desiredfj v vapor pressure by Vmeans'of aheat-er.r 31.` The vaporized E Q is caused to pass centrally through thecondenser 32 and is positioned therein by means of pulleys 34- anrl 36.As the insulated wire is passing through the condenser 32 it is heatedto a temperature in the neighborhood of 200 C. by means of an inductionheating element as shown at 38 in theV drawing. The resultant hotinsulated heated wire decomposes the nickel carbonyl as itpasses throughthe coating area. As the nickel coated wire leaves the coating area itpasses over pulley 35 and into a reducing or inert atmosphere furnace 50wherein the nickel coating is sintered. T he sintered nickel coated wirethen passes over pulley 52 and is spooled on reel S4. The Alunduminsulation is quite porous therefore the surface deposition conditionshave to be controlled in order to maintain the proper insulationconditions between the heater and the cathode. These depositionconditions can be controlled by carrier gas flow rate and the wiretemperature as it passes through the coating area. The nickel filmthickness deposited can if desired be adjusted by regulating the rate ofnickel carbonyl evaporation. For example, continuous nickel coating of a0.001 tungsten wire insulated with aluminum oxide to a thickness of .003can be successfully accomplished by using a helium iow rate of 7 cubicfeet per hour and a surface temperature on the wire of approximately 200C. By this method a nickel coating can be placed on the wire having athickness of approximately 0.0001 to 0.0002. The resulting nickel coatedwire can then be electrophoretically coated with triple carbonates toform a completed cathode assembly. In some cases it has been foundadvantageous to tire the nickel coated units in hydrogen at atemperature of about 950 C. This increases the conductivity along thefilm and thus makes it possible to use an even thinner film of nickel. n

By using these vapor deposition techniques both in the case of nickeland tantalum it has been found that no substantial diffusion of themetal will take place into the Alundum and high electrical resistancebetween the tungsten core and the metal film has been noted whileexcellent conductivity along the kmetal film is achieved.

While the above description and drawings submitted herewith disclose apreferred and practical embodiment of the quick heating cathode of thisinvention it will be understood by the speciiic details of constructionand arrangement of parts as shown and described are by way ofillustration and are not to be construed as limiting the scope of theinvention.

What is claimed is:

suitable for use as a thermionically emissive cathode in an electrondischarge device which comprises electrophoretically coating a heaterwire with Alundum, continuously passing the cooled wire through achamber containing nickel carbonyl while maintaining the wire in thechamber at 200 C. to obtain a nickel sheath thereon, passing the Wire sotreated through a chamber maintained at about 950 C. cooling the treatedwire and continuously coating it with a thermionically emissivematerial.

2. The method of manufacturing a composite material suitable for use asa thermionically emissive cathode in ari-electron discharge device whichcomprises electrophoretically coating a tungsten wire with Alundum,continuously depositing nickel on said Alundum coating by passing thecoated tungsten wire through a chamber containing nickel carbonyl whilemaintaining the wire in said chamber at approximately 200 C., passingthe nickel coated wire through a sintering furnace maintained at atemperature in excess of 900 C. and continuously coating the sinteredmaterial with a thermionically emissive material.

3. The method of manufacturing a composite material suitable for use asa thermionically emissive cathode in an electron discharge device whichcomprises electrophoretically coating a tungsten Wire with Alundum,continuously depositing nickel on said Alundum coating by passing thecoated tungsten wire through a chamber containing nickel carbonyl whilemaintaining the Wire in said chamber at approximately 200 C., passingthe nickel coated wire through a sintering furnace maintained at atemperature in excess of 900 C. and continuously coating the sinteredmaterial with a triple carbonate.

References Cited in the tile of this patent UNITED STATES PATENTS1,818,909 Reerink Aug. 11, 1931 2,075,910 Robinson Apr. 6, 19372,118,186 Farnsworth May 24, 1938 2,442,863 Schneider June 8, 1948 OTHERREFERENCES y Cline et al.: Journal of the Electrochemical Society,

October 1951, pp. 385 to 387.

1. THE METHOD OF MANUFACTURING A COMPOSITE MATERIAL SUITABLE FOR USE ASA THERMIONICALLY EMISSIVE CATHODE IN AN ELECTRON DISCHARGE DEVICE WHICHCOMPRISES ELECTROPHORETICALLY COATING A HEATER WIRE WITH ALUNDUM,CONTINUOUSLY PASSING THE COOLED WIRE THROUGH A CHAMBER CONTAINING NICKELCARBONYL WHILE MAINTAINING THE WIRE IN THE CHAMBER AT 200* C. TO OBTAINA NICKEL SHEATH THEREON, PASSING THE WIRE SO TREATED THROUGH A CHAMBERMAINTAINED AT ABOUT 950*. C. COOLING THE TREATED WIRE